Serotonin Synthesis and Uptake in Symptomatic Patients With Crohn's Disease in Remission

Background & Aims: Symptoms resembling irritable bowel syndrome (IBS) are reported frequently in Crohn's disease (CD) patients in remission. Studies of the mucosal content of serotonin, which is a pivotal neurotransmitter in the gut, suggest that serotonin availability is altered in IBS patients. We aimed to study the role of serotonin in the generation of IBS-like symptoms in CD patients in remission. Methods: Ileal and colonic biopsy specimens were obtained from 20 CD patients in remission, 10 with and 10 without IBS-like symptoms, and 11 healthy controls. Enterochromaffin cells were counted, and messenger RNA expression levels of tryptophan hydroxylase (TpH)-1 and serotonin reuptake transporter were determined. Results: The levels of mucosal serotonin reuptake transporter expression were significantly higher in the ileum than in the colon, in all groups studied (P < .02). When the ileum and colon were analyzed separately, TpH-1 expression in the colon of CD patients with IBS-like symptoms was found to be significantly higher compared with the 2 other studied groups (controls, P < .005; CD patients without IBS-like symptoms, P < .01). The number of enterochromaffin cells per gland was comparable for the patient groups in the ileum and colon. Conclusions: CD patients in remission who experience IBS-like symptoms have increased mucosal TpH-1 levels in the colon, suggesting that increased serotonin biosynthesis in the colon plays a role in the generation of the symptoms.